Novel, effective interventions for anorexia nervosa (AN) are much-needed (1) given that medical complications are common, the mortality rate is extremely high (2), and little data support the efficacy of any particular treatment for adults wit AN (3). Low motivation has predicted treatment drop-out (4) and outcome (4, 5). Motivational Interviewing (MI) is a well-supported approach to increase motivation in other highly ambivalent populations (6), and Ecological Momentary Interventions (EMI) also show promise to promote behavior change in other domains (7). The current proposal aims to investigate the effect of a novel EMI using motivational interviewing (MI) techniques to increase motivation and reduce AN symptoms in participants with AN/subthreshold AN. Additionally, behavioral health research has demonstrated that the effectiveness of messages may be affected by the framing of the message (8) and that message framing is most effective when it matches motivation orientation, i.e., approach-oriented individuals respond to gain-framed messages and avoidance-oriented individuals respond to loss-framed messages (9,10). However, research regarding message framing and motivation orientation is lacking for AN. This project will also test how framing and regulatory fit (i.e., congruence between goal and motivation orientation) impact MI effects. A two-study design will be employed. In the first study, N = 4 participants with AN/subthreshold AN will participate in a controlled single case alternating treatment study during which they will receive a random sequence of intervention and no-intervention phases prior to treatment. In the second study, N = 20 participants in the first six months of outpatient cognitive behavioral therapy for AN/subthreshold AN will undergo a randomly alternating sequence of intervention and no-intervention phases. In both studies, participants will receive personalized motivational text messages on their EMI device before meal times and at other stressful times during the intervention phases. Participants will receive gain-framed and loss-framed versions of the same personal reason to change. No messages will be received during no-intervention phases. Data regarding motivation orientation will be collected at baseline and participants will fill out kilocalorie intake records, motivation questionnaires, and ED symptom questionnaires throughout the testing phase on the EMI device. Data analysis appropriate to repeated-measures assessment will test hypotheses regarding the intervention and framing effects. The overarching goal of this proposal is to develop the applicant's abilities as a research scientist with extensive skills and a conceptual base in intervention research, with a focus on the benefit of technologically-based, ecological momentary methods for treatment research. Relevant research, coursework, hands-on training, and mentorship will support the applicant's goal to become a research scientist in this area.